The present invention generally relates to optical lens assemblies and, more particularly, to lens assemblies especially useful in projection televisions.
A projection television set typically includes three cathode ray tubes (CRTs), corresponding to the colors red, blue and green. A projection lens assembly uses a plurality of optics, which are typically plastic or glass elements, to magnify the image appearing on the CRT faceplate and project that image onto a much larger viewing screen. Typical CRTs used in projection televisions typically have a diameter of 3 to 9 inches. The image projected onto the screen generally has a size ranging from 40 to 60 inches or larger measured diagonally. Each of the CRTs must provide maximum brightness or light intensity and, to facilitate this objective, each CRT operates at maximum power to produce maximum light output at the faceplate while still maintaining color balance. As a result, the CRTs generate considerable heat within the enclosure of the projection television set. It is not uncommon for the ambient temperature in the interior of the television set to be elevated by 40xc2x0 C. to 45xc2x0 C. or more above room temperature.
Each CRT has an associated magnifying lens system mounted adjacent to the CRT faceplate. In one illustrative system, the lens assembly is formed with at least one xe2x80x9cAxe2x80x9d optic or element, at least one xe2x80x9cBxe2x80x9d optic or element and at least one xe2x80x9cCxe2x80x9d optic or element. Regardless of the number of optics, these are generally referred to in the art as xe2x80x9cAxe2x80x9d, xe2x80x9cBxe2x80x9d and xe2x80x9cCxe2x80x9d optic groups. That is, each xe2x80x9cgroupxe2x80x9d may be comprised of one or more optics. The xe2x80x9cBxe2x80x9d optic group usually includes an optic formed of glass, while the xe2x80x9cAxe2x80x9d and xe2x80x9cCxe2x80x9d optic groups may be formed of plastic, such as a molded acrylic plastic. However, it should be understood that each group may comprise one or more optics formed of glass and one or more optics formed of plastic.
There may be various types of forces exerted on an optic or by an optic that can lead to undesirable changes in the optical properties of the optic. Plastic optics are especially prone to thermal expansion due to heating by, for example, an associated CRT. As a result, the optic support structure can cause a thermally expanded optic to distort. Also, optics can distort due to forces exerted during assembly. This is also particularly true of plastic optics. Due to the physical changes in one or more of these optics, the focus of the lens system can change. The picture displayed on the television screen could then become blurred as a result of the defocusing effect of these types of optic distortions. Problems of this type are becoming even more acute and numerous as thinner optics are used in lens systems.
For at least these reasons, there is a continuing need for lens assemblies which address the effect of heat induced and/or assembly related focusing problems while, for example, maintaining relatively low cost and complexity associated with manufacturing the lens assemblies.
The present invention generally provides a lens cell, especially useful in projection televisions, including a tubular optic support structure having an interior with a longitudinal central axis and a first annular support surface extending around the longitudinal central axis. This first annular support surface receives a first optic having an outer circumferential edge. The first annular support surface includes at least one resilient member configured to contact the outer circumferential edge and to be moved in a radially outward direction, relative to the longitudinal central axis, by the first optic. The compliant or resilient nature of this member assists in preventing substantial movement of or forces on remaining portions of the tubular optic support structure by the optic. This feature is especially helpful during assembly of the lens cell and during use of the lens cell in a heated environment, such as a projection television cabinet, which causes the optic to thermally expand. The force exerted by the resilient member or members is not enough to distort the optic but is enough to retain the optic in a stationary condition within the optic support structure.
The first annular support surface is preferably positioned within a groove in the interior of the optic support structure and the circumferential edge of the first optic is received in the groove. Although the resilient member may be any member which facilitates the intended function, such as metal springs, separate rubber or other elastomeric inserts or molded rubber or elastomeric members, the preferred structure is a flexible tab member in the form of a cantilever. More preferably, four cantilevered members are used at equidistant, spaced locations surrounding the first optic. These members are molded into the wall of the tubular optic support structure.
The resilient member or members, such as the flexible tab members used in the preferred embodiment, provide a preload on the first optic by being resiliently biased in a radially outward direction when the first optic is assembled within the tubular optic support structure. That is, the resilient member or members move in a radially outward direction and then bear against the circumferential edge of the optic to provide a force directed radially inward against the optic. When that optic expands during use due to heat generated by the CRT or another heat source, the thermal expansion of the optic is accommodated by the resilient member or members without inducing further significant stress on remaining portions of the optic support structure.
In the preferred embodiment, the lens system includes four optics, however, many configurations and different numbers of optics may be used instead. In the preferred assembly, at least the plastic optics are mounted within structure including one or more resilient members for mounting each optic, as discussed generally above.
Additional objectives, advantages and features of the invention will become more readily apparent to those of ordinary skill in the art upon review of the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings.